In the extensive prior art relating to Coriolis-type mass flow meters with vibrating bodies consisting of tubes, there are only two basic tube shapes, namely straight tubes and arbitrarily bent or even twisted tubes, among which, for technical reasons, the U-shaped tube loops, i.e., those with a straight inlet tube with inlet end and with a straight outlet tube with outlet end as well as with a tube bend interconnecting the inlet tube and outlet tube, are the preferred tube shapes. With both tube shapes, for reasons of symmetry, use is generally made of two tube loops which extend parallel to each other in two parallel planes in the state of rest.
One of the two variants of mass flow meters, the one with two parallel straight tubes, is described, for example, in U.S. Pat. Nos. 4,768,384 and 4,793,191, which are incorporated herein by reference, and the other variant, with two parallel U-shaped tube loops, is described, for example, in U.S. Pat. No. 4,127,028.
In each of the two first-mentioned U.S. Pat. Nos. 4,768,384 and 4,793,191, the following features are described together: mass flow meter
with a vibrating-body arrangement working on the Coriolis principle through which flows a fluid to be measured and which comprises the following parts: PA1 with driver electronics for the vibration exciter, and PA1 with evaluation electronics PA1 with a vibrating-body arrangement working on the Coriolis principle through which flows a fluid to be measured and which comprises the following parts: PA1 with driver electronics for the vibration exciter, and PA1 with evaluation electronics PA1 with a vibrating-body arrangement working on the Coriolis principle through which flows a fluid to be measured and which comprises the following parts: PA1 with driver electronics for the vibration exciter, and PA1 with evaluation electronics PA1 with a vibrating-body arrangement working on the Coriolis principle through which flows a fluid to be measured and which is designed to be installed in a conduit and comprises the following parts:
a first straight tube having an inlet end and an outlet end, PA2 a second straight tube having an inlet end and an outlet end, PA2 a vibration exciter which sets the two straight tubes into opposite sympathetic vibrations in the plane containing the axes of the straight tubes, and PA2 two sensors spaced along the straight tubes for sensing the vibrations of the latter, as well as PA2 which determine the mass rate of flow from the phase difference of the sensor signals and/or the density of the fluid from the vibration frequency. PA2 a first U-shaped tube loop and PA2 a second U-shaped tube loop PA2 a vibration exciter which sets the two tube loops into opposite sympathetic vibrations perpendicular to their respective planes, and PA2 two sensors spaced along the straight tubes for sensing the vibrations of the latter, PA2 which determine the mass rate of flow from the phase difference of the sensor signals and/or the density of the fluid from the vibration frequency. PA2 a U-shaped tube loop consisting of PA2 a second mount which is provided at the transitions from the inlet and outlet tubes to the associated tube bend, is firmly connected with the first mount, and PA2 a vibration exciter mounted in the middle of the two straight tubes PA2 and a sensor mounted between the straight tubes for sensing the vibrations of the latter, PA2 which determine the mass rate of flow from the phase difference of the sensor signals. PA2 a first tube loop and PA2 a second tube loop which PA2 a plate mounted at the transitions from the inlet and outlet tubes to the associated tube bend and having holes which correspond to the outside diameter of the straight tubes and the tube bends and PA2 at least one vibration exciter which sets the two tube bends into opposite sympathetic vibrations perpendicular to their respective planes, and PA2 at least two sensors spaced along the straight tubes for sensing the vibrations of the latter
which two tubes extend parallel to each other in the state of rest, PA3 which extend parallel to each other in two parallel planes in the state of rest and each consist of PA3 a straight inlet tube with an inlet end, PA3 a straight outlet tube with an outlet end, PA4 which ends are fixed in a common mount, and PA3 a tube bend interconnecting the respective inlet tube and the respective outlet tube, PA3 a straight inlet tube with an inlet end, PA3 a straight outlet tube with an outlet end, PA4 which ends are fixed in a common first mount, and PA3 a tube bend interconnecting the inlet tube and outlet tube, PA3 in which the straight tubes are fixed to determine a vibration node, PA3 which sets the tubes, fixedly linked at this point via a spacing piece, into parallel sympathetic vibrations in the plane containing the axes of the straight tubes, PA3 each lie in one plane, PA3 are congruent and each consist of PA3 a straight inlet tube with an inlet end, PA3 a straight outlet tube with an outlet end, PA4 which ends are fixed in a common mount, PA3 and a tube bend interconnecting the inlet tube and the outlet tube, PA3 in which the latter are fixed to determine a respective vibration node,
On the other hand, the following features are described together in the above-mentioned U.S. Pat. No. 4,127,028: mass flow meter
Each of the two variants of mass flow meters has its advantages, but also disadvantages. Mass flow meters with U-shaped tube loops are not self-discharging in all mounting positions, and they are not nearly as insensitive to vibrations stemming from the conduit as mass flow meters with exclusively straight tubes. In addition, due to the Coriolis forces, the tube loops are subject to distortion out of the plane defined by their rest position.
Mass flow meters with exclusively straight tubes are, under certain circumstances, more sensitive to thermal shock as those with U-shaped tube loops, and the dependence of the measurement result on the pressure of the fluid may be stronger than with U-shaped tube loops, which becomes particularly apparent in case of variations in the pressure of the fluid.
In JP-A 3-48729 and the abstract thereof, a few features of mass flow meters with straight tubes and a few features of mass flow meters with U-shaped tubes are described together: mass flow meter
The invention as claimed serves to eliminate the above-mentioned disadvantages by providing a mass flow which combines the advantages of the two above-mentioned variants cleverly and better than the last-mentioned prior art mass flow meter.